It has long been known that a wide variety of polymeric additives can be used to produce asphalt and bitumen containing compositions (generally referred to as "polymer modified asphalt" compositions - PMA compositions) having certain enhanced properties. All types of asphalt, both naturally occurring and synthetically manufactured, are suitable for use in this invention. According to the present invention, the term "asphalt" is meant to also be inclusive of materials designated by the term "bitumen" and no distinction is made herein between the two terms. Naturally occurring asphalt is inclusive of native rock asphalt, lake asphalt, etc. Synthetically manufactured asphalt is often a by-product of petroleum refining operations and includes air-blown asphalt, blended asphalt, cracked or residual asphalt, petroleum asphalt, propane asphalt, straight-run asphalt, thermal asphalt, etc.
Asphalt has both viscous properties, which allow it to flow, and elastic properties, which resist flow. At high temperatures, the viscous properties dominate and the asphalt tends to flow or deform. At low temperature, the elastic properties dominate and the asphalt tends to resist flow. By adding certain polymers, these natural characteristics of asphalt can be modified. The properties improved by the addition of polymers are resistance to high temperature thermal deformation ("creep" or "rutting"), as well as resistance to cracking or deforming under repeated loadings, and, perhaps, the ability to use reduced amounts of asphalt in asphaltic aggregate compositions without loss of desired properties.
Goodrich, U.S. Pat. No. 5,331,028, issued Jul. 19, 1994, and assigned to Chevron, relates to a PMA composition comprising asphalt, a glycidyl-containing ethylene copolymer and a styrene/conjugated diene block copolymer. The Goodrich PMA composition can be used in preparation of asphalt concrete and is said to have enhanced resistance to thermal and pressure induced deformation.
Another Goodrich patent, U.S. Pat. No. 5,306,750, issued Apr. 26, 1994, and assigned jointly to Chevron and Du Pont, relates to a thermoplastic polymer-linked-asphalt product said to evidence enhanced performance properties even at low polymer concentrations. Among the polymers which can be used in the PMA compositions of both Goodrich patents are reactant polymers containing an epoxide moiety which is said to react with the asphalt. Preferred polymers for both Goodrich compositions are of the generalized formula: EQU E--X--Y
E symbolizes an ethylene copolymer unit. X symbolizes a polymer unit of the formula: EQU --CH.sub.2 --C(R.sub.1)(R.sub.2)--
wherein R.sub.1 is hydrogen, methyl or ethyl, and R.sub.2 is --C(O)OR.sub.3, --OC(O)R.sub.3, or --OR.sub.3, and wherein R.sub.3 is a lower alkyl group. Y symbolizes a copolymer unit of the formula: EQU --CH.sub.2 --C(R.sub.4)(R.sub.5)--
wherein R.sub.4 is hydrogen or methyl, and R.sub.5 is an epoxide-containing moiety of the formula ##STR1##
The polymers used in the PMA compositions of these two Goodrich patents are said to be well known in the art and are described, for example, in U.S. Pat. No. 4,070,532, issued Jan. 24, 1978 and in U.S. Pat. No. 4,157,428, issued Jun. 5, 1979, both by Clarence F. Hammer and both assigned to Du Pont. The polymers described in the Hammer patents and incorporated into the PMA compositions of the Goodrich patents include a polymer modifier known by the trade name, ELVALOY.TM. AM, available from Du Pont. ELVALOY.TM. AM is characterized by Du Pont as a polymer modifier to extend asphalt pavement life and to provide improvements in asphalt compatibility, mix stability, handling characteristics and product performance. Chevron makes available a PMA composition which contains the Du Pont ELVALOY.TM. AM, typically at polymer levels of about 1-3% by weight of the PMA composition.
Other processes for forming asphaltic products have been known to utilize acid treatment in conjunction with the addition of certain other earlier known polymers. For example, Benjamin S. Santos, U.S. Pat. No. 5,288,392, issued Feb. 22, 1994, relates to a process for converting acid sludge from waste oil refineries into an intermediate for production of asphaltic mixtures. The acid sludge is described as containing such non-specifically defined components as resinous and asphaltic materials and undefined hydrocarbon polymers. However, the unidentifiable polymers contained in this acid sludge are not related structurally or chemically to the polymers described by the Goodrich and Hammer patents or to the specific polymers used according to the present invention.
Three patents have issued to Lyle E. Moran, U.S. Pat. No. 4,882,373, issued Nov. 21, 1989 (Moran I), U.S. Pat. No. 5,070,123, issued Dec. 3, 1991 (Moran II), and U.S. Pat. No. 5,095,055, issued Mar. 10, 1992 (Moran III), which all relate to premodification of asphalt with an acid, such as HCl and H.sub.3 PO.sub.4, and then subsequent addition of a thermoplastic block copolymer.
Specifically, Moran I is said to improve the tensile properties of asphalt compositions by contacting asphalt with a mineral acid, bubbling an oxygen-containing gas through the acid treated asphalt, adding a thermoplastic elastomer to the treated asphalt and finally adding an unsaturated functional monomer to the polymer modified asphalt. Moran II and III dispense with the use of oxygen-containing gas and elaborate on a variety of acids and polymers which may be added to the asphalt composition to improve its storage stability. The processes of the Moran II and III patents are said to yield a more highly stabilized PMA composition by adding the acid simultaneously with or subsequent to the addition of the polymer.
In addition, Moran III acknowledges an earlier German Offen. 2 255 173 by Shell, published May 16, 1974, which relates to the addition of styrenic thermoplastic elastomers and small amounts of phosphoric acid or hydrochloric acid to asphalt to produce stabilized PMA compositions.
Other patent disclosures contain further descriptions of various acid and polymer treatments of bituminous or asphaltic materials. According to U.S. Pat. No. 4,368,228 of Romolo Gorgati, issued Jan. 11, 1983, bitumen obtained from acid sludge produced by concentrated sulfuric acid treatment of heavy distillates of asphalt-based petroleum is mixed with certain thermoplastic polymers to prepare prefabricated waterproofing membrane for roofing materials. U.S. Pat. No. 3,915,730 of Jean Lehureau, et al., issued Oct. 28, 1974, describes a surface paving material which is a composition of matter comprising 2,2-bis (4-cyclohexanol) propane diglycidyl ether, and a curing agent with a bituminous material derived from treatment of petroleum with boiling sulfuric acid.
Processes for acidic treatment of asphaltic or bituminous materials without the additional presence of polymers are related by two patents to Gordon Schneider, U.S. Pat. No. 4,238,241, issued Dec. 9, 1980 and U.S. Pat. No. 4,331,481, issued May 25, 1982. According to the Schneider patents, the amount of asphalt required in asphalt compositions or in asphalt and aggregate compositions is said to be decreased by the addition of sulfonic acid to the hot composition mix, without any detrimental effects on the strength and durability of the final paving material.
Each of these patents describe certain ways of improving the properties of a variety of asphaltic and bituminous materials. However, there is still a need for PMA compositions which are able to achieve high stiffness values at high ambient temperatures while at the same time maintaining needed low temperature stiffness properties.
According to the present invention, it has unexpectedly and surprisingly been discovered that the use of certain acids in the formulation of PMA compositions using certain polymers as described by the Goodrich and Hammer patents (and particularly ELVALOY.TM.) provides advantageous benefits to the process of formulating the PMA composition and also lends desirable properties to the resultant PMA composition. The PMA compositions of the present invention can be used for long wearing paving and other applications in climatic zones having a wide range of high summer and low winter temperatures without unacceptable thermally induced creep and/or crack problems.
Currently, standardized specifications and test methods for asphaltic binders are in a state of transition. The asphalt industry, Federal Highway Administration (FHWA), and individual state transportation departments are converting to specifications and test methods developed over several years by the Asphalt Research Output and Implementation Program of the Strategic Highway Research Program (SHRP). The SHRP specifications and test methods have been recommended by the FHWA to be in general, although voluntary, usage for materials for all state and federal highway programs by 1997. The PMA compositions of the present invention have all been tested and their properties and use characteristics have been determined according to the most recent SHRP specifications and test methods, in addition to many standard PMA tests. The specific tests methods are described in detail in publication "SHRP-A-370" titled "Binder Characterization and Evaluation Volume 4: Test Methods" This volume is published by the Strategic Highway Research Program of the National Research Council headquartered in Washington, D.C. The specific test methods used to identify the improved properties of this invention are: AASHTO TP5 Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR), and AASHTO TP1 Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR). AASHTO is the American Association of State Highway and Transportation Officials.
SHRP asphalt binder specifications are based primarily on properties related to performance of the laid down pavement, particularly in regard to performance under varying pavement conditions of imposed weight load and temperature. SHRP asphalt binder specifications are designed around the climatic conditions in the region where the asphalt composition will be used. SHRP test methods measure properties that are, based on SHRP supported research, believed to be directly correlated to pavement performance.
The testing used for the SHRP specifications measures the temperature range over which a given asphalt exhibits the properties qualifying it as an acceptable pavement binder for a given set of temperature and traffic conditions. These specifications utilize measurements of the complex shear modulus (G*), which represents total applied stress (.tau..sub.total) and total strain (.epsilon..sub.total), along with the phase angle (.delta.), which characterizes the viscoelastic nature of the binder. Expected pavement performance is then represented by a combination of G* with delta: G*/sin (.delta.), also known as 1/J", for minimum high temperature stiffness (to resist permanent deformation) and G*.times.sin (.delta.), also known as G", for maximum intermediate temperature stiffness (to reduce fatigue cracking). Various SHRP performance grades (PG) have been established according to the criteria of the testing.
Specific criteria for SHRP performance grades and the tests used in determining them are described below. FIGS. 1 and 2 provide SHRP specifications for performance grades PG 52-10 through PG 82-40. The two numbers that designate the SHRP grade bracket the temperature range, the SHRP DELTA (SHRP .DELTA.), over which a given SHRP asphalt grade exhibits the performance properties that have been established by SHRP. If one simply adds together the absolute values of the two temperatures that identify the high and low temperatures where all SHRP criteria are met, the SHRP .DELTA. is calculated. For an asphalt that conforms to a SHRP grade PG 64-22, one would add 64+.vertline.-22.vertline.and arrive at a value of 86 degrees. One can, however, take this process one step further. Applying statistical analysis to the data generated from the SHRP asphalt binder tests, one can calculate the exact temperatures at which an asphalt binder will conform to the high and low temperature SHRP requirements. In essence one can determine a precise SHRP grade for any given asphalt binder and in so doing be able to calculate a precise SHRP .DELTA. for that asphalt binder. For example, the asphalt binder above which conforms to a SHRP grade PG 64-22 could have a SHRP .DELTA. that equals 91.degree. C. if the high temperature specification were met at exactly 67.degree. C. and the low temperature specification were met at exactly -24.degree. C. A precise SHRP grade for this material would be PG 67-24 and the SHRP .DELTA. would be 91 degrees. Generally speaking to achieve a SHRP .DELTA. of 98 degrees or greater will require some type of asphalt modification, and only high quality conventional asphalt binders will exhibit a SHRP .DELTA. between 92 degrees and 98 degrees.
Dynamic Shear, AASHTO TP5, is determined both before and after simulated aging in the Rolling Thin Film Oven (RTFO) test to determine a minimum binder stiffness as exhibited in freshly paved roads up to one year in age and after the Pressure Aging Vessel (PAV) test to determine the maximum binder stiffness as exhibited in a pavement up to 5 or more years of age.
Bending Beam Creep Stiffness, AASHTO TP1, is determined after RTFO and PAV aging. The Bending Beam Creep Stiffness test measures low temperature stiffness characteristics. A 5".times.1/4".times.1/2" beam of binder material is molded, cooled to testing temperature, and subjected to an imposed weight load. Load versus deflection data is collected for 240 seconds. The low temperature specification values are based on the stiffness value determined at 60 seconds and the absolute value of the slope (m-value) of the time vs. log (stiffness) curve determined at 60 seconds.
Direct Tension, AASHTO TP3, is also determined after RTFO and PAV aging. The Direct Tension test measures per cent strain at low temperatures. A "dogbone" shaped specimen is elongated at low temperature, at a constant strain rate, until it fractures. The test is generally not performed unless the Bending Beam Creep Stiffness test passes the slope requirement and fails the stiffness requirement.